Your initial results are suggestive and it's a hypothesis I'd like to believe.But so far the proof isn't there.

You have no way to directly measure the strength of the grounds liquid.The effective extraction is being measured by one guy's nose and taste buds.These are presumably not done blind so inadvertant bias could play a role.

You boiled coffee slurry in a microwave on and off for 8 minutes and it tasted okay? Really??

One way to try and tease out a temperature effect:Brew three samples identically at, say, 24% brew ratio.Then dilute them with water at the slurry temperature to 6%, 12%, and 18% just before seperation from the grounds.If the strengths are still proportional to the brew ratios then the temperature variation isn't an issue.This would also help to exclude any possible effect concentration might have on extraction.

This might not work either, though. Maybe you'd end up with grounds liquid that is stronger than what's in the cup.

Except for inference, by taking a press, then squeezing to try and get the last bit of drippings and checking the strength. So far, this is a coin toss within +/-0.02% on the VST of the produced coffee.

Regardless, it can't be "yield" based extraction for immersion brews, otherwise your resulting extraction would be based on whether you took one or three cups out of your press pot and used that for a basis.

One alternative hypothesis is that there is grounds water that is bound in some fashion that does not contain the same concentration of dissolved solids. If that were true then squeezing the grounds wouldn't reveal it. You could infer it by measuring the effective extraction but the only tool you have for that is your taste.

Suppose I give you a cup of drip brewed coffee at a standard strength and ask you to estimate the extraction yield.How accurately can you reliably do it? Within 1%? Within 2%? Within 4%?

Netphilosopher Said:

So that's the challenge:

Use a press pot (the pretty much common immersion method that most people can do)- even heating the water, insulation, etc., and a steep time <=10 minutes, and attempt to produce a brew at 18% brew ratio that achieves 5.2% strength per a VST coffee refractometer.

Proposed would be actually 4 samples, set to same grind. I don't think it matters whether it's fine or medium. I'd probably avoid extremely coarse grind.

I think this could be done in either a Press Pot or an AeroPress.

If in an AeroPress:

Start out with a 12:60 brew (24%). Obtain a strength.Brew with 12:60 (24%), just before pressing, top off to 67g of water at same temp as the brew, probably around 175°F (18%), quickly stir and press, then obtain a strength.Brew with 12g:60, just before pressing, top off to 100g of water (12%), quickly stir and press, and obtain a strength.Brew with 12g:60, just before pressing, top off to 200g of water (6%), quickly stir and press, and obtain a strength.

If the dilution is pure enough, and the original brew achieved a strength of ~4.00%, then, the other three strengths should simply end up as diluted versions of the original strength (3.6%, 2.4%, 1.2% respectively). Departure from this relationship implies a brew ratio effect. That seem right?

Regardless of taste, if it were physically possible to extract to 30%, the immersion hypothesis indicates a limitation in strength.

If we consider 30% extraction the rough physical limit for coffee extraction for any coffee, then we're not picking subjective evaluations of what is "ideal", or a "sweet spot", or "over extracted". There is a testable limit for which any brew will be below.

If there is enough data at maximum extraction, then this limit can be adjusted if we start seeing data points above the prescribed line.

The other interesting thing is that increasing the absorption term increases the curvature from straight (immersion hypothesis) to quite non-linear at very high brew ratios and percolation settings for absorption. So not only can we test the limit itself, but we can test the shape.

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